Let's roll up our sleeves and solve this. We have 642 and we're going to multiply it by 205, essentially adding 642 to itself 205 times.
Step 1: 0 + 642 = 642
Step 2: 642 + 642 = 1284
Step 3: 1284 + 642 = 1926
Step 4: 1926 + 642 = 2568
Step 5: 2568 + 642 = 3210
Step 6: 3210 + 642 = 3852
Step 7: 3852 + 642 = 4494
Step 8: 4494 + 642 = 5136
Step 9: 5136 + 642 = 5778
Step 10: 5778 + 642 = 6420
Step 11: 6420 + 642 = 7062
Step 12: 7062 + 642 = 7704
Step 13: 7704 + 642 = 8346
Step 14: 8346 + 642 = 8988
Step 15: 8988 + 642 = 9630
Step 16: 9630 + 642 = 10272
Step 17: 10272 + 642 = 10914
Step 18: 10914 + 642 = 11556
Step 19: 11556 + 642 = 12198
Step 20: 12198 + 642 = 12840
Step 21: 12840 + 642 = 13482
Step 22: 13482 + 642 = 14124
Step 23: 14124 + 642 = 14766
Step 24: 14766 + 642 = 15408
Step 25: 15408 + 642 = 16050
Step 26: 16050 + 642 = 16692
Step 27: 16692 + 642 = 17334
Step 28: 17334 + 642 = 17976
Step 29: 17976 + 642 = 18618
Step 30: 18618 + 642 = 19260
Step 31: 19260 + 642 = 19902
Step 32: 19902 + 642 = 20544
Step 33: 20544 + 642 = 21186
Step 34: 21186 + 642 = 21828
Step 35: 21828 + 642 = 22470
Step 36: 22470 + 642 = 23112
Step 37: 23112 + 642 = 23754
Step 38: 23754 + 642 = 24396
Step 39: 24396 + 642 = 25038
Step 40: 25038 + 642 = 25680
Step 41: 25680 + 642 = 26322
Step 42: 26322 + 642 = 26964
Step 43: 26964 + 642 = 27606
Step 44: 27606 + 642 = 28248
Step 45: 28248 + 642 = 28890
Step 46: 28890 + 642 = 29532
Step 47: 29532 + 642 = 30174
Step 48: 30174 + 642 = 30816
Step 49: 30816 + 642 = 31458
Step 50: 31458 + 642 = 32100
Step 51: 32100 + 642 = 32742
Step 52: 32742 + 642 = 33384
Step 53: 33384 + 642 = 34026
Step 54: 34026 + 642 = 34668
Step 55: 34668 + 642 = 35310
Step 56: 35310 + 642 = 35952
Step 57: 35952 + 642 = 36594
Step 58: 36594 + 642 = 37236
Step 59: 37236 + 642 = 37878
Step 60: 37878 + 642 = 38520
Step 61: 38520 + 642 = 39162
Step 62: 39162 + 642 = 39804
Step 63: 39804 + 642 = 40446
Step 64: 40446 + 642 = 41088
Step 65: 41088 + 642 = 41730
Step 66: 41730 + 642 = 42372
Step 67: 42372 + 642 = 43014
Step 68: 43014 + 642 = 43656
Step 69: 43656 + 642 = 44298
Step 70: 44298 + 642 = 44940
Step 71: 44940 + 642 = 45582
Step 72: 45582 + 642 = 46224
Step 73: 46224 + 642 = 46866
Step 74: 46866 + 642 = 47508
Step 75: 47508 + 642 = 48150
Step 76: 48150 + 642 = 48792
Step 77: 48792 + 642 = 49434
Step 78: 49434 + 642 = 50076
Step 79: 50076 + 642 = 50718
Step 80: 50718 + 642 = 51360
Step 81: 51360 + 642 = 52002
Step 82: 52002 + 642 = 52644
Step 83: 52644 + 642 = 53286
Step 84: 53286 + 642 = 53928
Step 85: 53928 + 642 = 54570
Step 86: 54570 + 642 = 55212
Step 87: 55212 + 642 = 55854
Step 88: 55854 + 642 = 56496
Step 89: 56496 + 642 = 57138
Step 90: 57138 + 642 = 57780
Step 91: 57780 + 642 = 58422
Step 92: 58422 + 642 = 59064
Step 93: 59064 + 642 = 59706
Step 94: 59706 + 642 = 60348
Step 95: 60348 + 642 = 60990
Step 96: 60990 + 642 = 61632
Step 97: 61632 + 642 = 62274
Step 98: 62274 + 642 = 62916
Step 99: 62916 + 642 = 63558
Step 100: 63558 + 642 = 64200
Step 101: 64200 + 642 = 64842
Step 102: 64842 + 642 = 65484
Step 103: 65484 + 642 = 66126
Step 104: 66126 + 642 = 66768
Step 105: 66768 + 642 = 67410
Step 106: 67410 + 642 = 68052
Step 107: 68052 + 642 = 68694
Step 108: 68694 + 642 = 69336
Step 109: 69336 + 642 = 69978
Step 110: 69978 + 642 = 70620
Step 111: 70620 + 642 = 71262
Step 112: 71262 + 642 = 71904
Step 113: 71904 + 642 = 72546
Step 114: 72546 + 642 = 73188
Step 115: 73188 + 642 = 73830
Step 116: 73830 + 642 = 74472
Step 117: 74472 + 642 = 75114
Step 118: 75114 + 642 = 75756
Step 119: 75756 + 642 = 76398
Step 120: 76398 + 642 = 77040
Step 121: 77040 + 642 = 77682
Step 122: 77682 + 642 = 78324
Step 123: 78324 + 642 = 78966
Step 124: 78966 + 642 = 79608
Step 125: 79608 + 642 = 80250
Step 126: 80250 + 642 = 80892
Step 127: 80892 + 642 = 81534
Step 128: 81534 + 642 = 82176
Step 129: 82176 + 642 = 82818
Step 130: 82818 + 642 = 83460
Step 131: 83460 + 642 = 84102
Step 132: 84102 + 642 = 84744
Step 133: 84744 + 642 = 85386
Step 134: 85386 + 642 = 86028
Step 135: 86028 + 642 = 86670
Step 136: 86670 + 642 = 87312
Step 137: 87312 + 642 = 87954
Step 138: 87954 + 642 = 88596
Step 139: 88596 + 642 = 89238
Step 140: 89238 + 642 = 89880
Step 141: 89880 + 642 = 90522
Step 142: 90522 + 642 = 91164
Step 143: 91164 + 642 = 91806
Step 144: 91806 + 642 = 92448
Step 145: 92448 + 642 = 93090
Step 146: 93090 + 642 = 93732
Step 147: 93732 + 642 = 94374
Step 148: 94374 + 642 = 95016
Step 149: 95016 + 642 = 95658
Step 150: 95658 + 642 = 96300
Step 151: 96300 + 642 = 96942
Step 152: 96942 + 642 = 97584
Step 153: 97584 + 642 = 98226
Step 154: 98226 + 642 = 98868
Step 155: 98868 + 642 = 99510
Step 156: 99510 + 642 = 100152
Step 157: 100152 + 642 = 100794
Step 158: 100794 + 642 = 101436
Step 159: 101436 + 642 = 102078
Step 160: 102078 + 642 = 102720
Step 161: 102720 + 642 = 103362
Step 162: 103362 + 642 = 104004
Step 163: 104004 + 642 = 104646
Step 164: 104646 + 642 = 105288
Step 165: 105288 + 642 = 105930
Step 166: 105930 + 642 = 106572
Step 167: 106572 + 642 = 107214
Step 168: 107214 + 642 = 107856
Step 169: 107856 + 642 = 108498
Step 170: 108498 + 642 = 109140
Step 171: 109140 + 642 = 109782
Step 172: 109782 + 642 = 110424
Step 173: 110424 + 642 = 111066
Step 174: 111066 + 642 = 111708
Step 175: 111708 + 642 = 112350
Step 176: 112350 + 642 = 112992
Step 177: 112992 + 642 = 113634
Step 178: 113634 + 642 = 114276
Step 179: 114276 + 642 = 114918
Step 180: 114918 + 642 = 115560
Step 181: 115560 + 642 = 116202
Step 182: 116202 + 642 = 116844
Step 183: 116844 + 642 = 117486
Step 184: 117486 + 642 = 118128
Step 185: 118128 + 642 = 118770
Step 186: 118770 + 642 = 119412
Step 187: 119412 + 642 = 120054
Step 188: 120054 + 642 = 120696
Step 189: 120696 + 642 = 121338
Step 190: 121338 + 642 = 121980
Step 191: 121980 + 642 = 122622
Step 192: 122622 + 642 = 123264
Step 193: 123264 + 642 = 123906
Step 194: 123906 + 642 = 124548
Step 195: 124548 + 642 = 125190
Step 196: 125190 + 642 = 125832
Step 197: 125832 + 642 = 126474
Step 198: 126474 + 642 = 127116
Step 199: 127116 + 642 = 127758
Step 200: 127758 + 642 = 128400
Step 201: 128400 + 642 = 129042
Step 202: 129042 + 642 = 129684
Step 203: 129684 + 642 = 130326
Step 204: 130326 + 642 = 130968
Step 205: 130968 + 642 = 131610

So, 642*205 = 131610